The present invention relates to a transmitter for generating a control signal for remotely controlling the operations of various instruments such as television receivers, audio sets, video tape recorders, toys, air conditioners, etc.
A remote control signal transmitter is a transmitter for controlling or changing the operation of an instrument which is to be controlled from a position that is remote from the place of the instrument. The control or change is effected by operating a desired key or switch in a keyboard section on the transmitter. The data for control or the data for change may be transmitted by infrared rays, electromagnetic waves or supersonic waves. At present, infrared rays are mainly used as transmission means.
The transmitted data are received by a receiver section of the instrument to be controlled, and are converted into an electric signal, as a control signal. For instance, data transmitted as an optical signal, by means of infrared rays, are converted into an electric signal by a photo-sensitive element in the receiver section. The information of the converted electric signal is decoded by a control circuit in the receiver section, and then, the operation of the instrument is controlled in response to the decoded data.
In such a remote control system, the semiconductor integrated circuit (hereinafter, referred to as "IC") has been also widely utilized. More particularly, in order to make a transmitter compact and light in weight, an IC for remote control is contained in the transmitter. The coding to an operated key or switch in the keyboard section, as well as a transmission of the key code data, are carried out by this IC.
In this case, when remote control signal transmitters are constructed for different instruments by using IC's having the same circuit construction, the following shortcoming may occur. For instance, assume that in one room there are three different instruments: a television receiver, a video tape recorder and an air conditioner. Suppose further that each instrument has its own remote control signal transmitter employing an IC. Let us consider the case where, in order to change a receiving channel of the television receiver, the corresponding key switch is pressed on the remote control signal transmitter for the television receiver. Then the IC contained in the remote control signal transmitter for the television receiver detects the pushed key switch and produces key code data corresponding to that key switch. The key code data is appropriately modulated and transmitted from the transmitter to the television receiver, in the form of, for example, infrared rays. The transmitted infrared rays are received by a control signal receiving section of the television receiver. The receiving section converts the received infrared rays into an electric signal corresponding to the key code data, to change the channel of the television receiver. At this moment, the transmitted infrared rays may be possibly received by the control signal receiving section of the video tape recorder and/or the control signal receiver of the air conditioner. If this should occur, the control signal receiving section of the video tape recorder and/or the air conditioner would also respond to the transmitted key code data. As a result, the operating of the video tape recorder and/or the air conditioner would be erroneously changed in response to the key code data for controlling the television receiver.
In order to obviate this disadvantage, a custom code which is inherent in the respective instruments is individually preset for enabling the individual pairs of the control signal transmitter and the control signal receiving section for a plurality of instruments to communicate with each other, so that one control signal transmitter having assigned one custom code may not control instruments having different assigned custom codes. More particularly, remote control IC in the transmitter, first outputs its preset code data for the instrument paired with that transmitter. Then, the remote control IC outputs key data code by use of the key switch for controlling the change of operation. The respective instruments have inherent custom code data preset individually therefor.
Accordingly, even if a plurality of instruments receive the control signal, only the instrument having custom code data coincident with the transmitted custom code data preset can be activated. The activated instrument can receive the subsequently transmitted key code data, and its operation is controlled according to information of the key code data. Whereas, an instrument whose custom code is not coincident with the transmitted custom code has its receiving section held inactive. Accordingly, it does not respond to the subsequently transmitted key code data, and an undesired change of operation can be avoided.
However, if a plurality of remote control signal transmitters, for a plurality of different instruments, are constructed by making use of IC's having the same circuit construction, there is a shortcoming. As the number of controlled instruments is increased, the number of external terminals increases on the IC used for presetting the custom codes. This is because the custom code is set by the external switches. More particularly, the custom code can be arbitrarily preset by means of a combination of logic signals of "1" or "0" (logic signal "1" represents a high level, while logic signal "0" represents a low level). However, the combination of signals must be provided to the IC in the process of manufacturing the instruments. For this purpose, external terminals on the IC serving as custom code selection terminal are unavoidable. If only one terminal is prepared for this external terminal, then only two kinds of the signal combination of "0" or "1" are available. This means that custom codes for two instruments only can be preset with a result that only two transmitters can be controlled.
Therefore, to produce transmitters for a large number of instruments by making use of the IC's of the same circuit construction, the number of external terminals on the IC would increase in accordance with the number of the instruments to be controlled. For instance, in order to produce 10 pairs of transmitter and instrument, 10 kinds of signal combinations are necessary, so that at least 4 external terminals are required. Consequently, as the number of pairs of transmitter and instrument is increased, the chip size and cost of the IC for remote control is increased due to the increase of the external terminals. As a result, the size and weight of the control signal transmitter also become large.